Jump to content


Very low FPS on Lm4


  • Please log in to reply
16 replies to this topic

#1 Mcknight

Mcknight

    Newbie

  • Members
  • Pip
  • 4 posts
  • Country:

Posted 04 August 2014 - 07:44 AM

Hello people,

I am very new to this forum though not new to airsoft. I have had a Lm4 for a few months now, worked fine untill about 2 months ago normally the fps was around 340-350 with 0.2 but it decreased in time. Now it's about 280 when it's having a good day does anyone have any idea of what the cause is of the decreasing fps? Also ones in a while the gun emptys the gasmagazine in one shot.

Mcknight out

#2 StealthTaskForce

StealthTaskForce

    Enthusiast

  • Members
  • PipPip
  • 227 posts
  • Gender:Male
  • Location:Tampa
  • Interests:Airsoft, Paintball, Sports, My girlfriend, Knives and Real Steel
  • Country:

Posted 04 August 2014 - 08:15 AM

What have you been filling the magazines with? Green gas or propane? Because if you're using propane without silicon oil, then the seals could be drying out over time which could cause the drop in fps as the gas is escaping out of other places instead of the one place it should be going. The fps being reduced could also be to a dirty barrel. Do you clean it at all? And if so, it should be with just soapy water and some kind of cotton cloth

#3 SR105

SR105

    Tech

  • KWA Staff
  • PipPip
  • 168 posts
  • Gender:Male
  • Location:Walnut, CA
  • Country:

Posted 04 August 2014 - 08:54 AM

Usually such a drastic loss in power is due to a leak in the gas system. Most likely the bucking has torn and is now venting gas. Take a look into the chamber and take a look at the condition of the hop up bucking.

#4 Chuck S

Chuck S

    Guru

  • Members
  • PipPipPipPip
  • 1,315 posts
  • Gender:Male
  • Location:Cleveland, Ohio
  • Country:

Posted 05 August 2014 - 02:20 AM

Vapor from the upper receiver indicates a leak if there's much of it.  The gun recoiling normally?  Or is it shuggish?

Magazines will vent gas when low and when the seals are bad -- loose valve or dried out o-ring(s) in the magazine.

Full fill of gas requires about 45 seconds.  Can't over fill 'em.

-- Chuck

#5 Mcknight

Mcknight

    Newbie

  • Members
  • Pip
  • 4 posts
  • Country:

Posted 06 August 2014 - 01:58 PM

Thanks For the reply guys! Yes i clean It after every game and I am using green gas. Ever 5-7 games i clean the mags out. Found out Why It was 'spewing' gas, It was because my silicone oil was to much of water base so It just froze and blocked the Valve. I do fill the mags till It stops 'sissing' so thats about 45-50 sec. So It must be the Bucking looks a bit tourned up to, i will try to find a ra-tech bucking or do You Guys have Any other suggestions?

Mcknight

Edited by Mcknight, 06 August 2014 - 01:59 PM.


#6 netpoc

netpoc

    Enthusiast

  • Members
  • PipPip
  • 185 posts
  • Gender:Male
  • Location:Central Coast, CA
  • Country:

Posted 06 August 2014 - 03:14 PM

Maple leaf Evo II

#7 Chuck S

Chuck S

    Guru

  • Members
  • PipPipPipPip
  • 1,315 posts
  • Gender:Male
  • Location:Cleveland, Ohio
  • Country:

Posted 06 August 2014 - 03:41 PM

Stock bucking works fine for me.

-- Chuck

#8 Mcknight

Mcknight

    Newbie

  • Members
  • Pip
  • 4 posts
  • Country:

Posted 11 August 2014 - 04:55 AM

Okay will buy a Maple leaf,but i got one more question : I can't get the delta ring off, it is really stuck, Do you guys have any idea how to solve this? Have tried heating it etc, but it's still stuck...

#9 netpoc

netpoc

    Enthusiast

  • Members
  • PipPip
  • 185 posts
  • Gender:Male
  • Location:Central Coast, CA
  • Country:

Posted 11 August 2014 - 08:07 AM

Heat it, put good pressure on the nut and give it a good tap to snap it free.

#10 Chuck S

Chuck S

    Guru

  • Members
  • PipPipPipPip
  • 1,315 posts
  • Gender:Male
  • Location:Cleveland, Ohio
  • Country:

Posted 12 August 2014 - 02:32 AM

Remember the LM4 upper receiver is not monolithic and you can twist it apart with too much torque.  Barrel is Locktited and needs lots of heat to soften it.

-- Chuck

#11 netpoc

netpoc

    Enthusiast

  • Members
  • PipPip
  • 185 posts
  • Gender:Male
  • Location:Central Coast, CA
  • Country:

Posted 12 August 2014 - 06:12 AM

Leave the bolt carrier and charging handle in the upper and leave the upper and lower attached. Lay the gun on its left side with the grip pointed to your body and the barrel nut just off the edge of a table/bench and that should hold everything together while you power the nut off. You may want to remove optics if they are not allowing the gun to lay flat on its side.

#12 Mcknight

Mcknight

    Newbie

  • Members
  • Pip
  • 4 posts
  • Country:

Posted 05 September 2014 - 07:52 AM

Okay thnx! worked out got the new bucking in. Though my gun is still spewing gas after the first mag in on a day and keeps doing this even though i put new mags in de reciever... any solutions?

#13 Chuck S

Chuck S

    Guru

  • Members
  • PipPipPipPip
  • 1,315 posts
  • Gender:Male
  • Location:Cleveland, Ohio
  • Country:

Posted 07 September 2014 - 03:38 AM

Welcome to the world of GBB valving and o-rings. You should disassemble, clean, lube, and reassemble the discharge valve.  Do the charging valve at the same time.  There are some good photo essays on how to do this.  An airsoft valve tool makes this fairly easy.

You need pure silicone oil for the o-rings.  Any petroleum based will damage them.

-- Chuck

Edited by Chuck S, 07 September 2014 - 03:39 AM.


#14 netpoc

netpoc

    Enthusiast

  • Members
  • PipPip
  • 185 posts
  • Gender:Male
  • Location:Central Coast, CA
  • Country:

Posted 07 September 2014 - 09:35 AM

 Mcknight, on 05 September 2014 - 07:52 AM, said:

Okay thnx! worked out got the new bucking in. Though my gun is still spewing gas after the first mag in on a day and keeps doing this even though i put new mags in de reciever... any solutions?

Try running it totally dry and see if that addresses the issue. As in wipe away any and all grease, oil, or other lube, then test. If that solves the issue, the put a drop of oil on the piston o-ring only.

#15 crowley

crowley

    Enthusiast

  • Members
  • PipPip
  • 104 posts
  • Country:

Posted 09 September 2014 - 01:10 AM

 netpoc, on 12 August 2014 - 06:12 AM, said:

Leave the bolt carrier and charging handle in the upper and leave the upper and lower attached. Lay the gun on its left side with the grip pointed to your body and the barrel nut just off the edge of a table/bench and that should hold everything together while you power the nut off. You may want to remove optics if they are not allowing the gun to lay flat on its side.

Or simply use a proper Vise Block ;)

#16 netpoc

netpoc

    Enthusiast

  • Members
  • PipPip
  • 185 posts
  • Gender:Male
  • Location:Central Coast, CA
  • Country:

Posted 09 September 2014 - 07:47 AM

That will most likely snap something in the upper receiver. It's been done...

#17 Chuck S

Chuck S

    Guru

  • Members
  • PipPipPipPip
  • 1,315 posts
  • Gender:Male
  • Location:Cleveland, Ohio
  • Country:

Posted 10 September 2014 - 03:14 AM

Yep, an AR15 upper receiver block may allow the thin sheet metal parts fo come apart.  Ya really need to melt the Locktite before attempting to remove the barrel nut.

-- Chuck




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users